This invention relates to an intake port structure for a multi valve engine and more particularly to an improved induction system for a multi valve engine.
It is acknowledged that the performance of an internal combustion engine can be improved, particularly at high speeds, by the use of multiple intake valves. Although four valve per cylinder engines are quite common, there are a number of advantages of employing five valve per cylinder with three intake valves. The excellent breathing capacity of a five valve engine is well acknowledged. However, because of the good breathing capacity of five valve engines, these engines may have a tendency to have poor performance at low and mid-range speeds. The reason for this is that the flow velocity through the three intake passages under these running conditions is extremely low and poor combustion and fuel vaporization can result. It has been, therefore, been proposed to provide some staging system so that the effective intake area of the engine is reduced when operating at low and mid-range speeds.
Although such staging systems significantly improve the performance of the engine at low speeds, they do give rise to some difficulties. For example, if the staging is accomplished by providing a throttle valve in each intake passage, then the cylinder head porting configuration and throttle valve arrangement can become complicated. If, on the other hand, two of the intake passages are siamesed and the third is left separate and a throttle valve is provided only the siamesed passage, it has been noted that mid-range performance can deteriorate. That is, it has been found with such an arrangement that there may be a dip in the torque curve of the engine at midrange. Since this is a commonly operated speed range for the engine, such an arrangement may not be acceptable.
It has been discovered, however, that this problem with midrange performance can be overcome by providing at least some communication between the intake ports even though they are basically separated. However, this can present some problems in connection with the forming of the interconnecting passageway and keeping it close to the intake valve seats, where it is most effective.
It is, therefore, a principal object of this invention to provide an improved porting arrangement for an engine having at least three intake valves.
It is a further object of this invention to provide an improved porting arrangement for an engine having at least three intake valves.
It is a further object of this invention to provide an improved porting arrangement for an engine having at least three intake valves wherein the port openings are all formed in the cylinder head and can communicate with each other through a passageway formed close to the valve seats.
In addition to the porting considerations previously described, the use of multiple intake valves, particularly if staging is employed, can give rise to certain difficulties in connection with the associated charge forming system. Specifically, if fuel injection and specifically port fuel injection is employed and a staged induction system is also incorporated, then it is very difficult to utilize a single fuel injector for spraying fuel into all of the intake passages. This can present some problems even if staging is not employed because it is difficult to position an injector and have its spray nozzle in such an orientation to insure that a uniform mixture is supplied to the combustion chamber under all running conditions. Alternatively, even if stratification is desired, the mixture allocation within the combustion chamber can be difficult.
It is, therefore, a still further object of this invention to provide an improved fuel injection system for an internal combustion engine having multiple intake ports.
It is a further object of this invention to provide an improved staged induction system for a multi valve engine embodying fuel injectors.